1. Field of the Invention
The present invention relates to processing oil used for a variety of applications, including rubber processing, and more particularly to processing oil which contains polycyclic aromatic hydrocarbon (hereinafter may be abbreviated as PCA)xe2x80x94a substance known to be toxic to the human bodyxe2x80x94in an amount of less than 3 wt. % and which exhibits excellent performance characteristics that are conventionally required. The present invention also relates to a method for producing the processing oil.
2. Background Art
Processing oil has a variety of uses, functioning as a lubricant or a solvent depending on use. Primarily, it is used for processing rubbers such as natural rubber and synthetic rubber. It also serves as an extender in rubber processing. Moreover, processing oil is used as a plasticizer for thermoplastic resins, a printing ink component, and a softening agent for reclaimed asphalt. In accordance with individual uses, processing oil has been required to possess appropriate physical and performance characteristics, such as viscosity, density, volatility, or compatibility with rubber. For example, processing oil used for processing rubber desirably has good compatibility with rubber to enhance processability, appropriate viscosity in accordance with use, and resistance to deterioration, and therefore, processing oils meeting these requirements have been preferred.
However, a problem arising from toxicity of PCA has recently demanded reduction of PCA content of processing oil; particularly, in processing oil used in automotive tires, because dust thereof causes environmental pollution.
Thus, processing oils of reduced PCA content are under development. For example, Japanese Kohyo Patent Publication No. 06-505524 discloses a rubber composition using processing oil having a low PCA content. However, the processing oil has a high viscosity, which imposes limitations on the application thereof.
European Patent No. 0489371 B1 discloses a method for producing low-PCA processing oil formed of a naphthene-aromatic hydrocarbon mixture through supercritical extraction by use of a medium such as carbon dioxide.
European Patent No. 417980 A1 discloses a method for producing low-PCA and high-aromatic hydrocarbon processing oil through two-step-extraction performed by use of a polar solvent. In this method, however, a primary extract, which serves as a starting material for a second extraction step, has a density nearly equal to that of the polar solvent and strong affinity to the polar solvent. Thus, predetermining extraction conditions is considerably difficult and extraction efficiency is disadvantageously low; for example, the maximum yield reported in working examples is 51%.
The present inventors have conducted earnest studies, and have found that processing oil of low PCA content which has excellent performance can be obtained by mixing a primary extract and lubricating base oil and subjecting the mixture to extraction with a solvent. The present invention has been accomplished based on this finding.
Accordingly, an object of the present invention is to provide a processing oil having a reduced content of PCAxe2x80x94which is toxic to the human bodyxe2x80x94and excellent performance characteristics, such as yielding rubber of high processability and bleeding resistance, which have conventionally been demanded of processing oils. Another object of the present invention is to provide a method for producing the processing oil.
In a first aspect of the present invention, there is provided a processing oil containing a polycyclic aromatic hydrocarbon in an amount of less than 3 wt. % and an aromatic hydrocarbon in an amount of 25 wt. % or more; having a kinematic viscosity at 100xc2x0 C. of 10-30 mm2/s, a density of 0.870-970 g/cm3, and a temperature for 5 vol. % recovery by distillation (hereinafter called xe2x80x9c5 vol. % recovery temperaturexe2x80x9d) of 370-530xc2x0 C.
In a second aspect of the present invention, there is provided a method for producing a processing oil having a content of polycyclic aromatic hydrocarbon of less than 3 wt. %, in which an oil mixture comprising an extract obtained through extraction from mineral oil by use of a polar solvent in an amount of 40-97 vol. % and lubricating base oil in an amount of 3-60 vol. % is subjected to extraction treatment making use of a polar solvent.
Preferably, the extraction treatment is performed through countercurrent extraction making use of furfural as an extraction solvent under the following conditions: a solvent ratio of 0.5-2.5, a top temperature of an extraction tower of 50-110xc2x0 C., and a bottom temperature of the same of 30-80xc2x0 C.
Preferably, the method is adapted to produce the processing oil of the first aspect of the present invention.
The processing oil according to the present invention contains polycyclic aromatic hydrocarbon in an amount of 3 wt. % or less; has excellent physical and performance properties; and is advantageously used in applications such as rubber processing oil, a plasticizer for thermoplastic resins, a printing ink component, or a softening agent for reclaimed asphalt. The present invention provides a method for producing the above processing oil at low cost and high productivity.
The processing oil according to the first aspect of the present invention will first be described.
The processing oil according to the present invention may assume any of a variety of compositions and characteristics in accordance with the intended use and the production method; however, the processing oil satisfies the following five essential requirements.
(1) Polycyclic Aromatic Hydrocarbon (PCA)
The processing oil according to the present invention must have a PCA content of less than 3 wt. %. In Europe, handling of mineral oil having a PCA content of 3% or more is under regulation due to carcinogenicity, and handling of processing oil is also limited accordingly. The PCA content shown herein is measured through a method of The British Petroleum Institute (IP346/92).
(2) Aromatic Hydrocarbon
The aromatic hydrocarbon content of the processing oil is 25 wt. % or more, preferably 35 wt. % or more, more preferably 45 wt. % or more. Aromatic hydrocarbon, which determines affinity and compatibility of processing oil to rubber and other materials, is preferably contained in a large amount. When processing oil is added to rubber, aromatic hydrocarbon contained in the processing oil enhances processability and extendability of rubber, and bleeding of a plasticizer from aromatic vulcanized rubber is effectively prevented. When processing oil is used as a component of printing ink, aromatic hydrocarbon contained in the processing oil is effective for enhancement of compatibility to a resin component. The aromatic hydrocarbon content is measured in accordance with ASTM-D2007.
(3) Viscosity
The kinematic viscosity of the processing oil at 100xc2x0 C. is 10-30 mm2/s, preferably 12-30 mm2/s, more preferably 13-25 mm2/s. When the viscosity is less than 10 mm2/s, physical properties at an ordinary state of vulcanized rubber produced by use of processing oil deteriorate, whereas when it is in excess of 30 mm2/s, processability and operability during blending processing oil with rubber or other materials decrease. The kinematic viscosity of the processing oil is measured in accordance with ASTM-D445.
(4) Density
The density of the processing oil is 0.870-0.970 g/cm3, preferably 0.900-0.960 g/cm3. The density must fall within an appropriate range, since the density differs considerably from a conventionally adapted range during blending of processing oil with rubber or ink, to thereby require modification of blending operation. The density of the processing oil is measured in accordance with ASTM-D4052.
(5) 5 Vol. % Recovery Temperature
Among the distillation properties of the processing oil, the 5 vol. % recovery temperature is 370-530xc2x0 C. When the temperature is lower than 370xc2x0 C., the processing oil becomes easily volatile to cause deterioration of physical properties of rubber after thermal aging, due to evaporation thereof. The 5 vol. % recovery temperature is considered to be an approximate index of viscosity, and when it is higher than 530xc2x0 C., the viscosity of the processing oil increases to thereby cause deterioration of operability during blending with rubber. The 5 vol. % recovery temperature is measured in accordance with ASTM-D2887.
When processing oil satisfies the above requirements, it can suitably be used as the processing oil according to the present invention. For example, it can suitably be used for producing natural and synthetic rubber having a low PCA content and as a plasticizer for thermoplastic resins. Furthermore, it may also be used as a printing ink component and a softening agent for reclaimed asphalt.
The method for producing processing oil according to the second aspect of the present invention will next be described.
As the extract serving as a starting material of the present invention, there may be employed general extracted oil from mineral oil that is obtained during a step for refining lubricating oil. Briefly, the extract may be produced through steps of distillation under normal pressure, distillation under reduced pressure, and solvent extraction of a variety of crude oils. During the step of solvent extraction, customary polar solvents such as furfural, phenol, and N-methylpyrrolidone may be used. Preferably, the extract contains no asphaltene. Furthermore, the extract preferably has a PCA content of 40 wt. % or less; an aromatic hydrocarbon content of 40 wt. % or more; a kinematic viscosity at 100xc2x0 C. of 10-60 mm2/s; a density of 0.900-1.200 g/cm3; and a 5 vol. % recovery temperature of 370-530xc2x0 C.
As the lubricating base oil serving as the other starting material of the present invention, there may be employed general lubricating base oil produced from mineral oil that is obtained during a step for refining lubricating oil. Specifically, the lubricating base oil may be produced by refining, which includes solvent refining, hydrorefining, or hydrocracking, or optional dewaxing, fractions obtained through steps of distillation under normal pressure, distillation under reduced pressure, and deasphalting of a variety of crude oils. Furthermore, the lubricating base oil preferably has a PCA content of 10 wt. % or less; an aromatic hydrocarbon content of 5 wt. % or more; a kinematic viscosity at 100xc2x0 C. of 5-70 mm2/s; a density of 0.860-1.000 g/cm3; and a 5 vol. % recovery temperature of 370-530xc2x0 C.
The extract and the lubricating base oil are mixed to thereby form an oil mixture serving as a starting material to be subjected to extraction treatment. The required mixing proportion of the extract based on the oil mixture is 40-97 vol. %, preferably 50-95 vol. %, and that of the lubricating oil is 3-60 vol. %, preferably 5-50 vol. %. The oil mixture comprising the above-described two fractions preferably has a PCA content of 40 wt. % or less; an aromatic hydrocarbon content of 25 wt. % or more; a kinematic viscosity at 100xc2x0 C. of 5-100 mm2/s; a density of 0.860-1.200 g/cm3; and a 5 vol. % recovery temperature of 370-530xc2x0 C. Preferably, the oil mixture also contains substantially no asphaltene.
The above-described oil mixture is subjected to extraction treatment by use of a polar solvent, to thereby obtain processing oil to be desired. The extraction treatment is preferably performed through continuous extraction, particularly preferably countercurrent extraction. No particular limitation is imposed on the polar solvent for extraction, and solvents such as furfural, phenol, or N-methylpyrrolidone may be used as the extraction solvent, with furfural being particularly preferred.
Although the conditions of extraction treatment are appropriately selected in accordance with factors such as the type of extraction, the solvent for extraction, and the oil mixture serving as a starting material for extraction, the extraction is suitably performed though countercurrent extraction by use of furfural as a solvent for extraction. In this case, the solvent ratio; i.e., the ratio of solvent to oil mixture, is 0.5-2.5, preferably 1.0-2.0; the temperature as measured at the top of an extraction tower (hereinafter called the xe2x80x9ctop temperaturexe2x80x9d) is 50-110xc2x0 C., preferably 60-100xc2x0 C.; and the temperature as measured at the bottom of the same (hereinafter called the xe2x80x9cbottom temperaturexe2x80x9d) is 30-80xc2x0 C., preferably 50-70xc2x0 C. In addition, preferably, the top temperature is not less than the bottom temperature.
Through the above-described treatment, PCA is separated for removal from the bottom of the extraction tower with other impurities. The solvent is removed from the fraction obtained from the top of the extraction tower, to thereby collect the resultant product. Subsequently, properties such as viscosity and 5 vol. % recovery temperature of the product are optionally adjusted through further treatment such as distillation, dewaxing, or secondary refining, to thereby obtain a desired low-PCA-content processing oil.
The processing oil according to the first aspect of the present invention is produced by appropriate selection of the above-mentioned conditions of production.